Post-deflection acceleration type color picture tube

ABSTRACT

A post-deflection acceleration type color picture tube wherein the diameter of dot-like phosphors formed on a phosphor screen on the inner surface of a face plate of a glass bulb is made smaller than the diameter of electron beams when impinging upon the phosphors, and therewith, wherein a non-luminescent black substance is deposited into gaps between the respective adjacent dot-like phosphors so as to fill up the gaps to provide the phosphor screen, whereby the brightness, contrast and color purity of a picture screen are enhanced and any deterioration in a picture due to halation is reduced.

United States Patent [1 1 Yamazaki [4 1 July 1,1975

[ POST-DEFLECTION ACCELERATION TYPE COLOR PICTURE TUBE [75] Inventor: Eiichi Yamazaki, Ichihara, Japan [73] Assignee: Hitachi, Ltd., Japan [22] Filed: Sept. 16, 1970 [21] App]. No.: 72,758

[30] Foreign Application Priority Data Oct. 1, 1969 Japan 44-77770 [52] U.S. Cl 313/408; 313/472 [51] Int. Cl H01j 29/32; HOlj 31/20 [58] Field of Search 313/408, 472

[56] References Cited UNITED STATES PATENTS 12/1970 Yoshida et a1. 313/70 C 10/ 1 971 Kaplan 8/1967 Kaplan 313/92 B OTHER PUBLICATIONS Television Engineering Fink Handbook,

McGraw-l-Iill Book Company, Inc., 1957, TK 6642 F5 in Scientific Library, pp. 15-46 and 15-47 cited.

Primary Examiner-Robert Segal Attorney, Agent, or FirmCraig & Antonelli [5 7] ABSTRACT A post-deflection acceleration type color picture tube wherein thediaineter of dot-like phosphors formed on a phosphor screen on the inner surface of a face plate of a glass bulb is made smaller than the diameter of electron beams' when impinging upon the phosphors, and therewith, wherein a non-luminescent black substance is deposited into gaps between the respective adjacent dot-like phosphors so as to fill up the gaps to provide the phosphor screen, whereby the brightness, contrast and color purity of a picture screen are enhanced and any deterioration in a picture due to halation is reduced.

2 Claims, 2 Drawing Figures POST-DEFLECTION ACCELERATION TYPE COLOR PICTURE TUBE This invention relates to color picture tubes and more particularly, to a post-deflection acceleration type color picture tube having a phosphor screen which is so constructed as to enhance the brightness, contrast and color purity of a picture screen and to reduce any deterioration in a picture due to the so-called halation.

Conventional color picture tubes have been operated in such a manner that a color selective electrode disposed in front of a phosphor screen in opposition thereto and the phosphor screen are maintained at the same electric potential, that an electron beam from an electron gun is focussed by apertures or slits formed in the color selective electrode, and that electron beams each being approximately equal in size to the aperture or slit are bombarded upon the phosphor screen. With such prior art color picture tubes, since the electronbeam transmission factor of the shadow mask is usually approximately to 18 percent in the case of eg a shadow-mask type color picture tube, the utilization factor of the electron beam radiated from the electron gun has been very poor, thereby to render the picture screen dark to the disadvantage. In order to eliminate such disadvantages, various measures for improvements, for example, the enhancemen t of brightness of the phosphors have been practiced. However, the low transmission factor of the color selective electrode for the electron beam has caused the most serious bottleneck, and there has not been attained any measure to fully meet the requirement.

Therefore, a color picture tube of the post-deflection acceleration type has been suggested in order to increase the transmission factor of ,the color selective electrode to thereby enhance the brightness. The postdeflection accelerating or post-focussing color picture tube is provided with a transmission factor .of the color selective electrode several times as large as that of the.

prior art tube and the electric potential-of the phosphor screen higher than that of the'color selectiveelectrode. A focussing electric field established thereby between the color selective electrode and the phosphor screen is used to focus electron beams having passed through the above-mentioned electrode, thereby obtaining a desired beam-diameter or beam-width for operation of the tube. Since the electron beams having passed through the color selective electrode are used after the focussing to the desired diameter or width, the transmission factor of the color selective electrode may be enlarged and hence a bright picture may be obtained.

Such post-deflection acceleration type color picture tubes, however, are scarcely put to practical use at present in spite of their advantage that they may accomplish pictures several times as bright as those in the prior art color picture tube of the conventional shadow-mask type. The greatest reason for the impracticability of the post-deflection acceleration type tubes exists in the deterioration of the picture on account of the so-called halation that is the damage of the contrast and color purity of the picture screen caused by secondary electrons generated from the color selective electrode.

It is accordingly an object of this invention to provide a color picture tube enhanced in the contrast and the color purity.

Another object of this invention is to provide a color picture tube preventing deterioration in pictures.

Still another object of this invention is to provide a color picture tube increased in the brightness of a pictween said dots or stripes being filled with a nonluminescent black substance.

Description will now be made with reference to the accompanying drawings, in which:

FIG. 1 is an enlarged sectional view of the essential portions of a prior art post-deflection acceleration type color picture tube; and

FIG. 2 is an enlarged sectional view of the corre- 'sponding portions of a post-deflection acceleration type color picture tube embodying the present invention.

' While in the'following description of the preferred embodiment a color picture tube of the shadow-mask type will be specifically referred to, the invention is not restricted only to the specific type but may be also applied to a chromatron type color picture tube.

Referring to FIGS. 1 and 2, the color picture tube of the post-deflection acceleration or post-focussing type will be explained in detail. 7

FIG. 1 shows the essential portion s of a'prio'r art shadow-mask type color picture tybe, in whichreference numeral 1 designates a face plate; 2 a phosphor screen consisting of a congregation of a plurality of phosphor dots 3 as phosphor elements; 4 a shadow mask; 5 aplurality of apertures formed in the shadow mask 4; and 6 electron beams which, after passing through the apertures 5, are focussed between the shadow mask 4 and the phosphorscreen 2 to'the dimensions hereinafter stated. More specifically, the electron beams 6 are focussed so that each beam diameter d, may become smaller than the diameter D, of the phosphor dot 3 when impinging upon the dots. the difference in size between the two diameters D, and d, is utilized as a tolerance for landing. With such construction, however, the phosphor dots 3 are applied and formed over substantially the entire surface of the phosphor screen 2. Hence, when secondary electrons (not shown) generated from the shadow mask 4 bombard on the phosphor screen 2, substantially the total amount of the secondary electrons will bring about luminescence of the phosphors, thus causing the color purity and contrast of a picture screen to deteriorate.

Now, an embodiment of the invention will be described with reference to FIG. 2. As shown in the figure, the diameter D of each phosphor dot 13 is made smaller than the diameter d of each electron beam 16 at the impingement of the focussed beam upon the phosphor dot 13. In addition, a non-luminescent black substance 18 is filled up into gaps l7 betwen the respective adjacent phosphor dots 13 of diameter D Thus, the phosphor dots l3 and the non-luminescent black substance 18 constitute a phosphor screen 12. Herein, when the diameter D; of the phosphor dots 13 is selected to be approximately equal to the conventional beam diameter d,, it will be possible to provide a tolerance for landing approximately equal to the prior art one and to obtain substantially the same brightness of the phosphor screen as in the prior art. Furthermore, even if the secondary electrons occurring from the shadow mask bombard on the phosphor screen 12, halation due thereto will be sharply decreased relative to that in the prior art since the occupying proportion of the phosphor dots on the phosphor screen is reduced when compared with that of the conventional color picture tube.

Still furthermore, such construction of the phosphor screen reduces the reflection thereof for external light, thus enabling remarkable improvements in the contrast of a picture along with the above-mentioned reduction in halation.

In order to more effectively attain the halation reducing effect, the post-deflection accelerating voltage ratio of approximately 4 to 5 as hitherto widely employed should be decreased to approximately 1.5 to 3.0. Then, the acceleration of the secondary electrons is reduced, and the halation preventing effect becomes great. Particularly, according to the present invention, the electron beams need not be focussed to the possible least diameter as has been in the prior art, but they only require to be larger in diameter than the phosphor dots. Also in this sense, it is unnecessary to make the postaccelerating voltage ratio very large. A concrete example will now be mentioned. With the post-deflection acceleration voltage ratio of 2.0 and the phosphor-screen voltage of 24 kV, the shadow-mask voltage becomes 12 kV. As a result, a voltage with which the secondary electrons appearing from the shadow mask are accelerated towards the phosphor screen, is 12 kV equal to the difference between 24 kV and 12 kV. When the thickness of aluminium films to be evaporatively deposited at the back of the phosphors is appropriately selected, the secondary electrons of such energy will be eliminated to such extent as hardly raising any problem in practical use.

As previously described, while the above explanation has been made of the shadow-mask type color picture tube, the invention is also applicable to a chromatron type color picture tube. More specifically, the phosphor screen is finished in such a way that the width of stripe-like phosphors as phosphor elements formed thereon is made smaller than that of slits in a color selective electrode and that the non-luminescent black substance is applied into the gaps between the adjacent linear phosphors. Thus, the chromatron type color picture tube accomplishing the previously-mentioned objects may be obtained.

What is claimed is:

1. In a post-deflection acceleration type color picture tube including a glass bulb having a panel portion, a funnel portion and a neck portion, a phosphor screen disposed on the inner surface of a face plate of said panel portion, and a color selective electrode disposed just in front of said phosphor screen inside said glass bulb, the improvement comprising said phosphor screen being provided with phosphor dots which are smaller in diameter than the diameter of the focussed electron beams reaching said phosphor screen, wherein gaps between the adjacent phosphor dots on said phosphor screen are filled up with a non-luminescent black substance, and wherein the post-deflection accelerating voltage ratio between said phosphor screen and said color selective electrode is 1.5 3.0.

2. In a post-deflection acceleration type color cathode ray tube including a phosphor screen disposed on the surface of a face plate and provided with a plurality of color phosphor elements, and a color selective electrode disposed in front of the phosphor screen, the phosphor screen being supplied with an electric potential higher than that of the color selective electrode so as to focus electron beams passing through the color selective electrode, the improvement comprising the phosphor screen being formed of spaced phosphor elements which are smaller in size than the focussed electron beams reaching the phosphor screen, a nonluminescent black substance filling the gaps between adjacent phosphor elements, and the post-deflection accelerating voltage ratio of the phosphor screen and the color selective electrode being L5 to 3.0. 

1. In a post-deflection acceleration type color picture tube including a glass bulb having a panel portion, a funnel portion and a neck portion, a phosphor screen disposed on the inner surface of a face plate of said panel portion, and a color selective electrode disposed just in front of said phosphor screen inside said glass bulb, the improvement comprising said phosphor screen being provided with phosphor dots which are smaller in diameter than the diameter of the focussed electron beams reaching said phosphor screen, wherein gaps between the adjacent phosphor dots on said phosphor screen are filled up with a non-luminescent black substance, and wherein the postdeflection accelerating voltage ratio between said phosphor screen and said color selective electrode is 1.5 - 3.0.
 2. In a post-deflection acceleration type color cathode ray tube including a phosphor screen disposed on the surface of a face plate and provided with a plurality of color phosphor elements, and a color selective electrode disposed in front of thE phosphor screen, the phosphor screen being supplied with an electric potential higher than that of the color selective electrode so as to focus electron beams passing through the color selective electrode, the improvement comprising the phosphor screen being formed of spaced phosphor elements which are smaller in size than the focussed electron beams reaching the phosphor screen, a non-luminescent black substance filling the gaps between adjacent phosphor elements, and the post-deflection accelerating voltage ratio of the phosphor screen and the color selective electrode being 1.5 to 3.0. 